A rectangular butterfly valve with dimensions bх = 1х2

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A rectangular butterfly valve with dimensions bх = 1х2 m blocks the exit from the tank (Fig. 15). At what distance do you need to position the axis of the shutter O so that when you open it at the initial moment, it is only necessary to overcome the friction in the hinges at a depth of water in tank N.
Given: bha = 1x2 m; N = 2.5m
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